<!--
 * @Description: 嵌套圆
 * @Author: zzj
 * @Date: 2021-08-17 09:46:06
 * @LastEditors: zzj
 * @LastEditTime: 2021-08-17 10:00:12
-->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>嵌套圆</title>
    <style>
        .outer,.inner{
            box-sizing: border-box;   /* width : padding + border + 内容 */
            border-radius: 50%;
        }
        .outer{
            width: 300px;
            height: 300px;
            border: 3px solid gold;
            margin: 0 auto;
            padding: 50px;
            transition: padding 2s;
        }
        .outer:hover{
            padding: 10px;
        }
        .outer .inner{
            width: 100%;
            height: 100%;
            border: 5px solid gold;
        }
    </style>
</head>
<body>
    <div class="outer">
        <div class="inner"></div>
    </div>
</body>
</html>